Process for recycling packings

ABSTRACT

A process for recycling of packings containing reactive residues wherein the packings are introduced into a cold zone and cooled until the residues contained therein solidify and are then crushed in the cooled state, the crushed packings are divided into a fraction containing the reactive residues and at least one further fraction, the residue-containing fraction is introduced into a mixing zone into which an agent reactive with the residues is simultaneously introduced, optionally together with a catalyst, the temperature in the mixing zone being held below the softening temperature of the residues and the reactive agent, and the resulting mixture of residue-containing fraction and reactive agent and optionally catalyst is brought to a temperature sufficient for reaction and reacted in a reaction zone.

This is a continuation of PCT/EP94/02483 filed Jul. 28, 1994.

BACKGROUND OF THE INVENTION

This invention relates to a process for recycling packings containingreactive residues, in particular cartridges for producing polyurethanefoam. In the process the packing materials are recovered and theresidues contained therein converted into reusable products.

Residue-containing packings as occur for example in great quantities inthe form of wholly or partly empty cartridges are increasingly becominga disposal problem. They cannot be dumped on disposal sites for reasonsof environmental protection since, the residues contained therein canpass into the atmosphere, the soil or the groundwater and lead toconsiderable damage there. The same holds for burning, which isfrequently incomplete in particular with chemicotechnical products andproduces great quantities of pollutants which can be bound only byelaborate measures, if at all. Burning thus leads to a great reductionin the volume of waste but does not necessarily solve the pollutionproblem.

Special problems arise when the residues contained in the packings arethemselves reactive and possible even toxic products, as is the case forexample with isocyanate-containing prepolymers for polyurethane foams.The same holds for other reactive plastic products, for exampleself-curing or hardenable mixtures for coatings, adhesive mixtures, etc.In the following the problem will be discussed in relation to thedisposal of prepolymer-containing cartridges for producing polyurethanefoams, this case being given only as an example.

Polyurethane foams have become widely used in many fields. They arecommonly used particularly in the construction industry for sealing andinsulating, as well as in other technical fields. Polyurethane foams arecommonly discharged from cartridges containing a polyurethane prepolymertogether with required additives. These cartridges cannot be reused. Onthe other hand, they are problem waste which cannot be disposed of inthe normal way.

In accordance with efforts to limit household and industrial waste,measures are being increasingly discussed and implemented to forcemanufacturers to take back their product packaging after use and ensureits reuse or disposal themselves. Such measures have made it necessaryto find ways of treating such waste economically. The treatment ofreturned cartridges for polyurethane foam production involves a numberof problems which complicate economic recycling. For example, somereturned cartridges can be under pressure due to the penetration ofmoisture during improper storage or treatment, which makes both openingand burning a problem. Furthermore the cartridges have different fillingconditions, ranging from overaged cartridges virtually full ofprepolymer which cannot be discharged due to a blocked valve, tovirtually empty cartridges with only a remainder of prepolymer adheringto the edges in an uncrosslinked to crosslinked state.

Up to now a number of processes have become known for recyclingpackings, including aerosol cans for polyurethane foam production. Forexample it has been proposed to pass pressure cans via a sluice systeminto a plant under inert gas and crush them there. Further, processeshave become known for passing aerosol cans into a plant, crushing themthere and extracting the ingredients with suitable solvents. In theseprocesses both the packing materials and the ingredients (prepolymer,propellant) are recovered.

However these known processes, some of which are quite efficient and inuse, are capable of being improved with regard to industrial safety,process control and efficiency. It is problematic to separate theresidues contained in the packings in simple fashion and direct them tosuitable reuse. Further problems arise from the fact that the packingscontain toxicologically unsafe substances as well as combustiblesolvents which can yield explosive gas mixtures after opening. Inparticular these processes are designed for recyclingpropellant-containing aerosol cans, however, which limits theirapplicability for pressureless cartridges.

SUMMARY OF THE INVENTION

The invention is therefore based on the problem of providing a processfor recycling packings, for example containers holding polyurethaneprepolymers in particular for foam production but also for adhesivepurposes, together with solvents, and recovering the useful materialscontained therein without releasing unhealthy and pollutive ingredientsin uncontrolled fashion and without the course of the process beingburdened by reactive components released from the packings. The processshould meet the requirements for industrial safety and in particularconvert reactive residues still contained in the packings into a formsuitable for direct further processing.

This problem is solved according to the invention by a process of theabove-mentioned type wherein the packings are introduced into a coldzone and cooled until residues contained therein solidify, the packingsare then crushed in the cooled state, the crushed packings are dividedinto a fraction containing the reactive residues and at least onefurther fraction, the residue-containing fraction is introduced into amixing zone into which an agent reactive with the residues issimultaneously introduced, optionally together with a catalyst, thetemperature in the mixing zone being held below the softeningtemperature of the residues and the reactive agent, and the resultingmixture of residue-containing fraction and reactive agent and optionallycatalyst is brought to a temperature sufficient for reaction and reactedin a reaction zone.

The inventive process makes it possible to open and process packings ina fully safe way. In particular it permits the various materialscontained in the packings to be separated safely. The reactive residues,for example isocyanate-containing prepolymers in cartridges forproducing polyurethane foam, are treated in a safe manner. Due to thefreezing of the ingredients contained in the packings there is neither areaction-induced pressure increase in the process nor undesirablereaction between reactive components. At the temperatures prevailing inthe process the presence of water is also harmless. The two latterpoints are of importance in treating isocyanate-containing products whenfor example damaged packings carry water into the process. At the sametime, reactive second components contained in so-called 2C foams, forexample glycols, carboxylic acids or water, can be easily introducedinto the process. The inventive process is thus suitable for treatingboth cartridges for 1C and 2C foams and transitional forms between thetwo simultaneously.

In the inventive process the packings, for example cartridges, are firstintroduced into a cold zone and cooled therein until the residuescontained, including any low-boiling solvents solidify. Temperatureslower than -80° C. to -100° C. are generally sufficient for thispurpose, but one expediently works in liquid nitrogen as a coolingmedium. In this case it is important that the process be performed inthe absence of oxygen to avoid condensation of liquid oxygen which couldhave an adverse effect in later process steps.

The packings are expediently introduced into the cold zone using acellular wheel pneumatic sluice which introduces the packing into aguide cage extending in the cooling medium. In the cold zone the packingis then guided a sufficient distance through the cooling medium toobtain complete freezing.

When the desired temperature is reached, generally the temperature ofliquid nitrogen, the packings are guided into the crushing zone wherethey are crushed in the cold state. The temperatures here shouldexpediently be under -80° C. to -100° C.; it might be necessary to sprayin liquid nitrogen or cold gaseous nitrogen.

Crushing is expediently done in a hammer mill working against a sifter.This achieves a shaking and fulling effect which not only crushes to adesired particle size but also separates the various materials: metal,paper, plastic and ingredients. It has surprisingly turned out that thepacking materials (metal, paper and plastic) can thereby be separatedextremely well from the ingredients (reactive residues andsolvents/additives in powder form), the ingredients being obtained asfine powder.

In a subsequent separating step the crushed packings are divided into aleast two fractions, one of which contains the reactive residuesincluding propellant in a solid state. This separating step expedientlyuses a sifter, preferably a riddle sifter, through which the finecomponents (mainly reactive residues and solvent) fall. Metal parts areseparated with magnetic methods, large plastic parts and scraps of papersieved out on the riddle sifter.

The frozen ingredients from reactive residues and solvent pass from theseparating zone into a mixing zone into which an agent reactive with theresidues is simultaneously introduced. Temperatures lower than -80° C.to -100° C. also prevail in this mixing zone to ensure the frozen stateof the introduced materials and solidify the sprayed-in reactive agentimmediately into a fine powder. This permits formation of a uniformmixture of ingredients in powder form and reactive agent, which cannotreact due to the prevailing temperature conditions. The temperatures inthe mixing zone are in any case below the melting point of both theresidues and the reactive agent.

A spray tower is expediently used as a mixing zone, the frozeningredients falling in from above. The reactive agent is sprayed intothis powder stream from lateral nozzles, preferably together with coldgaseous nitrogen to ensure the necessary low temperatures. It isexpedient to precool the reactive agent but it must remain sprayable.

It can be expedient to spray in the reactive agent together with acatalyst which promotes the reaction with the reactive residues of thepackings. This is generally unnecessary with isocyanate-containingprepolymers, however, since the isocyanate-containing mixtures alreadycontain such catalysts.

The powdery mixture of ingredients and reactive agent and optionallycatalyst is then guided into a reaction zone which consists for exampleof a conveyer belt moving continuously under the mixing zone. The powdercollecting here is then brought to a temperature sufficient for reactionis order to react. Any solvents contained evaporate at this point andare condensed out at a suitable place, which is no problem when nitrogenis used as a cooling medium. To give the reaction product the desiredform the conveyer belt can have lateral limits. For separating thereaction product from the conveyer belt is it possible to provideparting means, for example suitable coatings or release paper. Theheating in the reaction zone is expediently done with microwaves, whichcause fast direct heating of the powder material from the inside to theoutside so that uniform degassing occurs.

Following the reaction zone one can provide further processing andtreating zones as well as a final sluice for passing out the reactedmaterial.

As mentioned above, the inventive process is especially suitable forrecycling residue-containing polyurethane foam cartridges. In this casethe reactive agent is in particular a hydroxy compound, for examplewater, ethylene glycol, propylene glycol, glycerol, oligomers andmixtures thereof as well as derivatives thereof. Ethylene glycol, waterand polyether alcohols are preferred, whereby in any case at least tworeactive hydrogen atoms should be present. Polycarboxylic acids canlikewise be used. Especially suitable polyether alcohols are theso-called Jeffamines™.

In recycling packings for producing polyurethane foams it isadvantageous to convert the isocyanate-containing prepolymers in theprocess itself into foam materials which can be used for example forinsulating purposes. The inventive process can thus continuously produceinsulation boards, whereby the propellants contained in the powderproduced in the mixing zone promote foam formation. It is also readilypossible to produce foils or to admix additives, for examplecellulose-containing materials, and then press these mixtures intocomposite materials during or after reaction. However it is preferableto produce granules from reacted material which are further processedlater.

The inventive process is especially suitable for recycling pressurelesspolyurethane foam cartridges which are emptied on site using a suitablepistol and then returned to the manufacturer for recycling. Thesecartridges, which are used both for 1C and for 2C foams, arepressureless during storage and generally contain no expanding orfoaming agent. If an improvement in foaming behavior is necessary andthis improvement cannot be achieved by using water as the secondcomponent, low-boiling solvents can be present, for example pentane,which are liquid at normal temperature but evaporate with the secondcomponent at the reaction temperatures of the prepolymer and produce anexpanding effect. The inventive process can likewise be used for aerosolcans for polyurethane foam production if an effective separation ofpropellant is ensured in the area of the reaction zone. The process isthus fundamentally suitable for packings which also contain expandingagents and achieve an expanding and/or foaming effect, optionally inaccordance with temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically an embodiment of a plant for carrying out theinventive process;

FIG. 2 shows the entrance area of the plant according to FIG. 1;

FIG. 3 shows the conveying, crushing and sorting part of the plantaccording to FIG. 1;

FIG. 4 shows the mixing and reaction zones of the plant according toFIG. 1;

FIG. 5 shows details of the feed by the cellular wheel sluice;

FIG. 6 shows details of the transport system guide in a horizontalprojection; and

FIG. 7 shows the guide of FIG. 6 in cross section.

The view of an embodiment of the inventive recycling plant shown in FIG.1 entry sluice 1 which is fed cartridges 13 to be treated via conveyorand sorting belt 11 (FIG. 5). The entry sluice is preferably formed as acellular wheel pneumatic sluice into chambers 12 of which cartridges 13fall from above via feed hopper 14 (FIG. 2). Rotation of cellular wheel1 causes the cartridges to pass into the lower area of the sluice and beejected laterally with the help of gaseous nitrogen GAN from pipe 15. Tomake this possible the cellular wheel rotates in a gastight containeropen at the top which can be subjected to pressurized gaseous nitrogenGAN from one side in its lower area so that cartridge 13 therein can beejected on the opposite side into guide system 21. The nitrogen supplyvia pipe 15 is preferably ensured with gaseous nitrogen from cold bath2. Obviously the rotational speed of cellular when 1 and the pressuresurges from nitrogen pipe 15 for ejecting the cartridges from thecellular wheel are mutually coordinated. The cellular wheel has for thispurpose a measuring sensor marked M.

From the cellular wheel the cartridges pass via guide 21 into cold bath2 filled with liquid nitrogen. Guide 21 expediently consists of anelongate basket construction open on all sides which permits unhinderedadmission of liquid nitrogen and escape of gaseous nitrogen. Details ofguide 21 and transport device 23 for transporting cartridges 13 will bedescribed more closely below in connection with FIGS. 4 and 5.

On their way through cold bath 2, which is supplied with fresh liquidnitrogen LIN in accordance with level via pipe 24 and has measuringsensor LIC for checking level, cartridges 13 are cooled to the bathtemperature. The cage structure of guide 21 ensures free admission ofcooling medium and quick discharge of produced gaseous nitrogen. Gaseousnitrogen is removed from the bath area via pipe 16 with the help ofventilator 17. The length of guide 21 and the transport speed areadjusted so that cartridges 13 are cooled to a sufficiently lowtemperature of at least -80° C. to -100° C. even when completely filledwith remainder.

Cartridges 13 are transported in guide 21 with the help of transportdevice 23 expediently consisting of circulating transport belt 25 withprotruding transport forks 26 which engage in guide 21 from above andpush cartridges 13 guided therein ahead of themselves. Transport rolls27 ensure precise guidance of transport forks 26. Forks 26 are disposedon transport belt 25 at intervals coordinated with the size ofcartridges 13 to be transported. Measuring unit M serves to monitor thetransport speed and its coordination with the feed rate of cartridges13.

After running through cold bath 2 cartridges 13 pass out of guide 21into conveying device 3 (FIG. 3) in the form of circulating conveyorbelt 31 having transport segments coordinated with the size ofcartridges 13. Conveying device 3 is preferably formed as a steepconveyor which receives cartridges 13 in the segments formed bytransport forks 33 disposed at regular intervals and releases themoverhead into crushing device 4. The conveyor belt is guided via rolls32 provided with measuring unit M for monitoring and controlling theconveying speed.

Crushing device 4 consists of a shredder or preferably hammer mill 41.Hammer mill 41 preferably works against a sifter to guarantee a certainparticle size of the crushed material. Sifter 42 simultaneously producesa fulling effect which promotes separation of the ingredients embrittledby the cold from the container material. Obviously one can add coolingmedium, preferably liquid nitrogen LIN, via pipe 43 for maintaining thenecessary low temperatures of -80° C. to -100° C. if temperature checkTK indicates an inadmissible rise in temperature. The working speed ischecked and controlled via measuring sensor M. Gaseous nitrogen isremoved via pipe 44 and recycled or blown off via valve 45.

From crushing device 4 the crushed material passes into sorting device5. This consists first of riddle sifter 51 on which coarse parts areseparated from fine parts. Coarse parts are mainly the crushed materialsof the container which are shaken off on inclined sifter 51 anddischarged from the process via a sluice not shown.

Powdery ingredients and fine parts of the container pass through riddlesifter 51 onto first magnetic separator 52 which separates remainingiron and aluminum components from plastic particles and ingredients. Onfirst magnetic separator 52 magnetic components are first separated andfed to first transport belt 53 which also receives the metal and plasticparts shaken off by sifter 51. Second transport belt 54 receivesplastics, ingredients and nonmagnetic metal parts, which are dividedinto metallic and nonmetallic fractions via second magnetic separator 55coupled with the transport belt. The metallic fractions pass onto firsttransport belt 53, the nonmetallic are guided directly into spray tower6. Cold gaseous nitrogen can be supplied via pipe 56 if temperaturecheck TIC indicates an inadmissible rise in temperature. Measuringsensors M check the working speed of all moving parts of separatingsystem 5. If the cartridges consist entirely of nonmetallic materialsthe magnetic separators can naturally be dispensed with.

Obviously a temperature of no more than -80° C. to -100° C. is ensuredboth in the crushing plant and in the sorting device by suitable feedingpipes for cooling medium, preferably nitrogen in gaseous or liquid form.

The powdery ingredients and plastic parts passing into spray tower 6(FIG. 4), and having a temperature of no more than -80° C. to -100° C.so that solvents contained therein are also present in a solid state,are mixed with reacting medium and optionally catalyst sprayed into theupper area of spray tower 6 via feed 61. The reacting medium, preferablyethylene glycol, is located in the liquid state in supply tank 62, thecatalyst in supply tank 63. Both tanks have metering units coordinatedtherewith.

Reacting medium from tank 62 and catalyst from tank 63 are sprayed intospray tower 6 via pipe 61 in dosed relation to the reactive ingredients,whereby a precooling stretch can be provided in the course of feedingpipe 61 for cooling the materials to a beneficial temperature (abovemelting point). However, the spray material solidifies within the spraytower itself at the temperatures of less than -80° C. to -100° C.prevailing there. For maintaining the temperature in the spray tower itis therefore expedient to introduce cooling medium additionally, forexample liquid nitrogen LIN via pipe 64 or gaseous nitrogen via pipe 65,if temperature check TIC indicates a need therefore. It is expedient tospray the cooling medium into the lower areas of the spray tower toensure additional swirling and mixture of reactive compound, catalystand reactive can content by cold nitrogen rising in spray tower 6.

From spray tower 6 the mixture of reactive cartridge content, reactivecompound and catalyst passes in powder form into reaction space 7.Within reaction space 7 there is reaction belt 71 for receiving thefalling material from spray tower 6 and guiding it into actual reactionzone 72 where the reaction is induced by heat. For this purpose heatelements 73 are disposed above conveyer belt 71 for heating the reactionmaterial on conveyer belt 72 with microwaves or infrared rays to atemperature sufficient for reaction, for example room temperature orthereabove.

To prevent reaction material 74, i.e. the mixture of reactive cartridgecontent, reactive compound and catalyst, from sticking to conveyer belt71 it may be expedient to cover the conveyer belt with separating foil75 which is wound off roll 76a and onto second roll 76b. The separatingfoil is optionally reusable.

On conveyer belt 71 the reaction material reacts into the particularproduct desired. At the same time solvents and adsorptively boundcooling medium nitrogen still contained in the mixture from the spraytower are released and sucked off via pipe 77 and directed to separationand solvent recovery (not shown). In the presence, or upon formation, ofa foaming agent, such as pentane or CO₂, the escape from reactionmaterial 74 causes partial foaming of the reaction material, which isnot undesirable for certain purposes.

At the end of conveyer belt 71 there is scraper 78 for detaching thereacted reaction material from the conveyer belt or separating foil, itbeing passed out of the process via product sluice 8 and taken away viaconveyer belt 81. Nitrogen pipes 81 and 82 regulate the protective gassupply in the sluice area, the protective gas used being expedientlynitrogen, which need not be cooled. Further nitrogen pipes 83 and 84 inthe area of the entrance and exit of separating foil 75 prevent oxygenfrom entering the system in this area. It is also unnecessary to suecool nitrogen here.

Obviously the inventive process is performed in a cold- andheat-insulated plant. In particular the entrance of oxygen must also beprevented in order to prevent liquid oxygen from condensing into coldbath 2. It is of advantage for the gas distribution to perform theentire process including spray tower 6 at temperatures at which solventand foaming agent exist in a solid state. This permits them to beremoved centrally via suction pipe 77 in reaction space 7 and directedto recovery. The reacted/cured polyurethane material emerging from theprocess in product sluice 8 can be directed to any desired further usein the form of granules. Possible uses are for example for insulatingmaterials and in composite materials.

FIG. 5 shows details of the sluice system at the entry of the process,the cellular wheel pneumatic sluice being rotated 90° relative to theview of FIGS. 1 and 2.

Cartridges 13 with polyurethane prepolymer residues intended for theprocess are introduced via conveyor and sorting belt 11 to cells 12 ofcellular wheel pneumatic sluice 1. Feed hopper 14, under which thesluice rotates away, ensures accurate introduction of cartridges 13.

Conveyor and sorting belt 11 expediently has ribs or forks 15 forseparating cartridges 13 transported on the conveyer belt from oneanother. One can thus exactly coordinate the cycle of cartridge releasewith the transport speed of cellular wheel sluice 1 and the transportcycle in guide 21 of cold bath 2 at a given conveying speed. The fixingof a cycle further allows cartridges 13 to be discharged from sluice 1in precisely timed fashion with the help of pressurized nitrogen throughpipe 15 (FIG. 2).

As evident from FIG. 5, pneumatic sluice 1 opens at its lower rend(opposite feed hopper 14) into guide 21 into which the cartridges slide,being ejected toward transport device 23 with the help of the pressuresurge from pipe 15.

FIGS. 6 and 7 show details of guide 21 and transport device 23 fortransporting cartridges 13 within guide 21.

Guide 21 has altogether an elongate, cage- or basket-like structure. Theguide consists substantially of parallel guide rails 22 which leaveenough room therebetween for the admission of liquid nitrogen and theescape of evaporated nitrogen. Guide rails 22 are held together byfixing rings 27 on the outside such that their relative position to oneother is fixed. The fixing rings encompass entire guide 21 with theexception of the upper end, where the space between two guide rails 22remains free so that transport fork 26 or the like can engage from aboveand push cartridges 13 located in guide 21 through the guide. Thisresults in the picture of an elongate cage comprising parallel rails 22and encompassing fixing rings 27 which leaves a free space over itsentire length in the upper area for motion of transport fork 26. Thesize of the cage is coordinated with the size of the cartridges andselected so that the cartridges cannot tilt when being guided through.In the drawing cartridge 13 is transported in the direction of the arrowwith the bottom first and fork 26 embraces fitting 18.

Transport forks 16 are located on transport belt 25 which transports thecartridges through guide 21 via a suitably disposed system of transportrolls 27 to conveyer belt 31, where they fall out of guide 21 and arereceived by transport elements 32 of conveyer belt 31. From the end ofguide 21 transport belt 25 is moved back above bath 2 toward cellularwheel sluice 1, where forks 26 again engage in guide 21 at the intendedplace and transport the cartridges located in the guide through bath 2.Obviously entire guide 21 extends in the area of the actual coolingstretch in cold bath 2 in such a way that the cartridges are washed byliquid nitrogen on all sides.

I claim:
 1. A process for recycling packings selected from cartridgesand cans containing polyurethane prepolymers, the process comprisingintroducing the packings into a cold zone and cooling the packings untilthe prepolymers contained therein solidify; crushing the packings in thecooled state; dividing the crushed packings into a fraction containingthe prepolymers and at least one fraction containing scrap of thepackings; introducing the fraction containing the prepolymers into aspray tower simultaneously with a hydroxy compound and optionally acatalyst, the temperature in the spray tower being below the softeningtemperature of the prepolymers and the hydroxy compound; and bringingthe resulting mixture of the prepolymer and the hydroxy compound and theoptional catalyst to room temperature or above and reacting theresulting mixture in a reaction zone.
 2. The process of claim 1 whereinthe temperature in the spray tower is below -80° C.
 3. The process ofclaim 1 wherein the process is performed in the absence of oxygen. 4.The process of claim 1 wherein the packings are cooled with liquidnitrogen.
 5. The process of claim 1 wherein the packings are cooled in acooling stretch.
 6. The process of claim 1 wherein the packings arecrushed at a temperature below -80° C.
 7. The process of claim 1 whereinthe prepolymers contained in the packings are pulverized duringcrushing.
 8. The process of claim 7 wherein the hydroxy compound issprayed into the pulverized prepolymers.
 9. The process of claim 1wherein gaseous or liquid cold nitrogen is sprayed into the spray towerfor temperature control.
 10. The process of claim 1 wherein the reactionzone is heated with microwaves.
 11. The process of claim 1 wherein gasesreleased in the reaction zone are separated by condensation.
 12. Theprocess of claim 1 wherein the hydroxy compound is ethylene glycol or apolyether alcohol.
 13. The process of claim 1 further comprisingintroducing additives into the spray tower.
 14. The process of claim 1further comprising introducing additives into the reaction zone.